1. Field of the Invention
The invention relates to permanent magnet designs that can generate very strong and highly homogeneous fields primarily for interventional and MRT use.
2. Description of the Related Art
In MRI interventional applications it is desirable to have a system that scans the patient while a surgeon accesses the patient just as on a surgical table and is guided by real-time images in order to perform the interventional procedures. Most MRI systems available today are not well suited for this purpose. The traditional cylindrical or solenoidal magnets prevent access to the patient whereas the open systems are not open enough and offer only limited access.
Although the ideal system to perform such procedures is probably a planar configuration it is not a very efficient geometry. Alternatively, a more enclosed system offers better homogeneity and stronger field. However, accessing the patient becomes more difficult and consequently a comprise system is required.
An eight-element Halbach ring array magnet, FIG. 1, with four of the alternate elements removed offers a suitable configuration. Such a system is depicted in FIG. 2 and provides three orthogonal paths to the central enclosure. These access paths are the one parallel to the cylindrical axis and the other two orthogonal access pathways are parallel to the plane perpendicular to the cylindrical axis. Of the two pathways perpendicular to the cylindrical axis, one path can be used for inserting a patient while the other, orthogonal path gives surgeons an easy access to the patient so that they can perform real-time guided interventional procedures during the MRI scan. This system forms a quadrupolar magnetization orientation with respect to the four elements and generates a dipolar field in the central enclosure. The design combines the benefits of a strong field in the imaging region while generating minimal fringe fields.
For whole-body scanning, the invention offers such an unprecedented opening in MRI magnet design, the very open, patient friendly environment enables the use of the magnet for routine diagnostic applications as well. Moreover, the opening is also ideal for weight bearing or stand-up patient positions and can be used in applications that require such patient loadings as well.
In contrast to more traditional magnet designs, permanent magnets offer a great advantage in terms of cost and maintenance requirements. The dominant MRI systems and in particular interventional systems are mostly based on superconducting technology. It is well known that these systems are expensive to purchase and maintain because of the expensive cryogenic fluids and parts that require periodic refilling and servicing. Therefore, the current invention offers an alternative with the capability of generating up to 1.0 Tesla or greater fields in imaging regions well above 40 cm DSV while keeping magnet size, weight and cost within reasonable limits.